Megasquirt II and two throttle bodies??

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t/abossfan
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Joined: Wed Jul 20, 2005 7:14 pm

Megasquirt II and two throttle bodies??

Post by t/abossfan »

Newbie here so be kind.

I will cut to the chase,

The build up I am planning will include two 4-barrel universal throttle bodies (leaning towards the accufab units). I will be using an old tunnel ram intake modified with injector bungs. I would assume the TPS units would not be a problem, I could run one as the throttle bodies are linked mechanically (correct me if I am wrong). What about the IAC valves/motors? Can two IAC valves be wired in and operate properly?

Thank you for your responses in advance.
t/abossfan
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Post by t/abossfan »

Lance,

Thank you for your response. I should also clarify that I will not be using the top piece of the tunnel ram intake that connects the front and rear carburetor air paths (on a v8 engine). The front throttle body will provide air for the front 4 cylinders and the rear throttle body provides for the back 4 cylinders without any airpath cross over/ connection between the two. Correct me if I am wrong but won't both IACs need to be operating? I haven't purchased the throttle bodies but two will be $$$$. I would like to know in advance if this is possible or just a fantasy.

Thanks again,


t/abossfan
eliotmansfield
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Post by eliotmansfield »

Remember you need a vacuum source also, sounds like you will need to make a t-piece between the two tb's. If you made a slightly bigger link between the two, say 1/2" you may be able to use one IAC setup.

i think driving two iac's will be tricky, unless you can do a simple open/closed solenoid setup.
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GotDart
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Post by GotDart »

t/abossfan wrote:I should also clarify that I will not be using the top piece of the tunnel ram intake that connects the front and rear carburetor air paths (on a v8 engine). The front throttle body will provide air for the front 4 cylinders and the rear throttle body provides for the back 4 cylinders without any airpath cross over/ connection between the two.
I'm not clear what you mean by this. Are you completely eliminating the plenum above the intake runners? If so, I believe having only one throttle bore per cylinder would be a major restriction. What size engine is this going on and what is the maximum expected rpm?
BottleFed70
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Post by BottleFed70 »

GotDart wrote:I'm not clear what you mean by this. Are you completely eliminating the plenum above the intake runners? If so, I believe having only one throttle bore per cylinder would be a major restriction. What size engine is this going on and what is the maximum expected rpm?
The lower part of a tunnel ram intake looks like it's actually an intake for dual 4bbl carbs. The big difference being that the front 4 cylinders are seperate from the rear 4cyln. Think of it as using 2 4cyln intakes on a V8.

t/abossfan: Megasquirt measures intake vacum to determine how much fuel to inject. Having the 4 front and rear cylinders seperate will cause major greif when it comes time for tuning. What you'll have to do is connect the 2 1/2's of the tunnel ram. Depending on your intake, you may be able to drill a 1" hole between the two 1/2's. Otherwise, you'll need to install some large vacum lines. Once you do this, you should be able to get by with only 1 IAC.
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GotDart
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Post by GotDart »

BottleFed70 wrote:The lower part of a tunnel ram intake looks like it's actually an intake for dual 4bbl carbs. The big difference being that the front 4 cylinders are seperate from the rear 4cyln. Think of it as using 2 4cyln intakes on a V8.
I know what a t-ram looks like, I have one sitting in my garage. 8)

My point is that it sounded like t/abossfan was eliminating the plenum altogether and mounting the throttle body directly to the lower half of the t-ram manifold. If that is the case, then it becomes more like an individual runner manifold where one throttle bore supplies all the air for one cylinder.

Consider that the 4150 style TB's typically have four 1-3/4" throttle bores and flow 1000-1200cfm. So one throttle bore could concievably flow 250-300cfm. A set of ported heads could easily out flow that, especially on a large displacement motor turning 6000rpm. However, using the 4500 series Doninator type TB with 2-1/4" throttle bore might be sufficient. I just don't have enough information to understand what t/abossfan is trying to do.
t/abossfan
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Tunnel Ram Manifold

Post by t/abossfan »

GotDart,

Sorry for the delayed response on this subject. I got my answer and have neglected to check the site. To answer your question for my manifold idea, the adapters I will be using will in affect make it a non-individual runner design. The adapters will have to be fabricated but it will be similar to an open carb spacer (probably be 1 inch thick). One will be used for the front for cylinders and a separate one will be used for the back cylinders. This will create a shared path for the air for the front 4 cylinders and a shared path for the rear 4 cylinders. However as mentioned previously in this thread the front and rear cylinders would not be shared.

Just setting the 4 barrel throttle bodies on top of the tunnel ram intake would not work. The ports do not match up perfectly and the throttle body butterflies hit the manifold. The spacer/adapter will bring the throttle bodies up off of the manifold and allow the butterflies to open.

As for engine, it will be a small block Ford 302, boss 302. Cleveland style, 4v, closed chamber heads with huge intake valves, 2.19 in. These things have to be spun up for power. I thought the tunnel ram would assist in this as the stock boss 302 intakes are a restriction above 6,000 or 6,500 rpm.

Thank you for your input.
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